Below is an eloquent description of the coil heater in an all wood unit versus glass lined.
The real culprit in making the wood hot is radiant heat energy. The hotter the coil, the more radiant energy it will emit. The glass provides no protection from the radiant heat energy. It will go right through the glass.The key is to not abuse the coil.
It is an energy balance equation. When you push the button, energy is released from the battery into the coil at a rate of speed determined by the charge left in the battery. You can remove that energy from the coil if your draw rate is at the correct speed. Too slow of a draw, and the extra heat energy will be radiated into the wood. Too fast, and you won't get a very good hit.
The flower roasting is also a energy balance equation. The entire mass of flower must be brought up to vaporizing temperature which takes more time with more mass. If you stop drawing on the tube while heat is still being applied, the flower mass will still be at vaporizing temperature and producing vapor. Some of that vapor will drop back down into the coil area if the tube is still connected. This may cause the coil/heater area to smell bad.
Continue to draw air after removing the heat until unit cools down and stops producing vapor. The high surface area of the coil removes the heat quickly, especially if you keep pulling after you release the button.
To put things in perspective, an automobile is something that can be damaged or destroyed if you run the engine too fast for too long. You don't do that because vehicles are expensive and you need your car!. But the better you treat your car, the longer it will last. The same can be said for vaporizers.
Our units will be modeled after the iHeat Instaheat Coil